1. Field of the Invention
The invention relates to an apparatus for testing the performance of a safety shut-off valve. In one aspect, the invention relates to a partial stroke valve testing apparatus having an activation key to adjust the apparatus from a testing position to an operating position and which can be locked in the testing position to indicate that the valve testing apparatus is in the testing condition. In another aspect, the invention relates to a partial stroke valve testing apparatus having a safety release mechanism which must be disengaged in order to place the apparatus in the testing position. In another aspect, the invention relates to a partial stroke valve testing apparatus having a remotely controlled and monitored test activation system.
2. Description of the Related Art
Industrial process plants, such as chemical plants and oil refineries, which utilize production piping and valving, are typically required to have safety equipment installed. This safety equipment includes emergency shutdown valves (ESD valves) which can be quickly closed to isolate sections of piping which may have developed a leak or some other safety problem. An actuator is attached to the ESD valve through a drive shaft which is turned by the actuator to quickly close a valve that generally remains open during production. Such actuators include “spring-to-fail” actuators, which are spring-biased to a “valve closed” position, but are maintained in a “valve open” position by air pressure. These valves automatically close under the influence of the spring in the event of a loss of air pressure. Air pressure loss can occur by a breach in the air pressure system resulting from an accident, or by the selective bleeding of the pressurized air by an operator in response to an emergency.
It is imperative that such valves are fully operational in the event of an emergency and, thus, it is necessary to periodically test the actuators and valves in order to insure that they are capable of operating properly in an emergency. However, a testing program that involves closing and opening all the safety valves in a production facility would significantly disrupt production and impose a substantial economic burden on the plant. One alternative is to utilize a bypass valve and piping around the ESD valve. When the bypass valve is opened, the ESD valve and its safety system can be fully tested without affecting production. However, space constraints and the additional cost in the bypass valve and piping may preclude this as an acceptable alternative.
A second alternative is the use of a partial stroke valve testing apparatus. This apparatus is typically inserted between the valve and the actuator, and enables the valve to be partially closed, thereby enabling all of the safety features to be tested but without interrupting production as would occur with fully closing the valve. A drive mechanism in the valve testing apparatus prevents the actuator from closing the valve more than a specified percentage of full closure when the drive mechanism is engaged. An example of such an apparatus is shown in FIG. 1, which is a perspective view of a prior art partial stroke valve test apparatus showing the interior components of the apparatus, and FIG. 2, which is a plan view of the prior art partial stroke valve test apparatus illustrated in FIG. 1.
Referring now to FIGS. 1 and 2, the valve testing apparatus comprises a hollow housing 200 defining a chamber 201 enclosing a drive cam 202. (The testing apparatus is normally provided with a cover, which has been removed in FIGS. 1 and 2 to show the interior components of the testing apparatus.) The drive cam 202 is fixedly attached to a drive shaft 206, shown in FIGS. 1 and 2, for example, as keyed together by a key 208 so that rotation of the drive shaft 206 will urge the rotation of the drive cam 202. The drive cam 202 is provided with a planar, radially-extending face 204.
Adjacent to the drive cam 202 is an engagement shaft 212 comprising an elongated, generally cylindrical member having a key end 203, a bearing end 205, and a longitudinal axis orthogonal to the longitudinal axis of the drive shaft 206. The engagement shaft 212 is provided with an asymmetrical engagement cam 210 having a shoulder 214 and a planar engagement cam face 216 orthogonal to the longitudinal axis of the engagement shaft 212. The engagement shaft 212 is seated in bearings in the housing 200 for rotation of the engagement shaft 212 and the engagement cam 210 within the housing 200.
A key hole 218 provides access to the key end 203 of the engagement shaft 212 and comprises a slot 222 for receipt of a key 220. The key 220 comprises a flattened, generally T-shaped body having a handle 228, and a shaft 230 extending generally orthogonally therefrom and terminating in a fork end 232 opposite the handle 228. The fork end 232 terminates in a pair of parallel, spaced-apart fingers 234 parallel to the shaft 230. A pair of spaced-apart wells (not shown) adapted for mating communication with the fingers 234 are provided in the end of the engagement shaft 212. The fork end 232 of the key 220 can be inserted through the slot 222 into the wells in the shaft 212, and the key 220 rotated 90°, thereby rotating the shaft 212 into a testing position. The fork end 232 is adapted to rotate 90° to the slot 222 so that removal of the key 220 will be prevented while the apparatus is in the testing configuration.
A detent mechanism is provided to position the engagement shaft 212 and the engagement cam 210 properly in the testing and operational positions. This comprises a detent seat 226 in the bearing end 205 which operably communicates with a spring-biased detent 224, which is a type well-known in the art and is mounted in the housing 200 in radial alignment with the engagement shaft 212. An operator turning the engagement shaft 212 with the key 220 will feel the action of the detent 224 engaging the detent seat 226 to indicate the proper positioning of the engagement shaft 212. The detent mechanism will also minimize the potential for the shaft 212 to inadvertently rotate.
The testing apparatus is inserted between an ESD valve and actuator so that the housing 200 is connected at a first side to a mounting flange on the valve bonnet and at a second side to the drive face of the actuator (not shown). The drive shaft 206 is operably connected to the ESD valve and actuator so that activation of the actuator will rotate the drive shaft 206, thereby operating the ESD valve.
As shown in FIG. 1, with the engagement cam 210 positioned so that the cam shoulder 214 is oriented away from the drive cam 202, the drive cam 202 can rotate past the engagement cam 210 when the drive shaft 206 is rotated, enabling the ESD valve to be fully closed in the event of an emergency. The valve testing apparatus is normally maintained in this operational condition so that the ESD valve is fully operational in the event of an emergency. However, when the engagement shaft 212 is rotated to a testing position so that the cam shoulder 214 is oriented adjacent the drive cam 202, rotation of the drive cam 202 during the test will bring the drive cam face 204 into contact with the engagement cam face 216, thereby preventing further rotation of the drive cam 202 and the drive shaft 206 and further closure of the ESD valve. Thus, the test can be performed by partially closing the valve without a costly interruption in plant production.
The engagement shaft 212 is rotated by inserting the first end 234 of the key 220 into the end of the engagement shaft 212 and rotating the key 220 90°. The position of the key 220 will provide some visual indication that the valve testing apparatus is in the testing condition. If the valve testing apparatus is inadvertently maintained in the testing condition, it will not operate properly in the event of an emergency.